In an optical communication system, it is generally necessary to couple an optical fiber to an opto-electronic transmitter, receiver or transceiver device and, in turn, to couple the device to an electronic system such as a switching system or processing system. These connections can be facilitated by modularizing the transceiver device. An opto-electronic transceiver module includes an opto-electronic light source, such as a laser, and an opto-electronic light receiver, such as a photodiode, and may also include various electronic circuitry associated with the laser and photodiode. For example, driver circuitry can be included for driving the laser in response to electronic signals received from the electronic system. Likewise, receiver circuitry can be included for processing the signals produced by the photodiode and providing output signals to the electronic system.
The electronic system can be provided with connectors or receptacles into which opto-electronic modules can be plugged. In some types of systems, receptacles are located on a front panel of the system enclosure or rack. In such systems, electrical connectors in the receptacles may be mounted on the edge of a circuit board inside the enclosure. In other types of systems, the receptacles or connectors are mounted on the surface of a circuit board. Such a connector arrangement may be referred to as a “mid-plane” or “mid-board” connector arrangement. Opto-electronic modules that can be mid-board mounted commonly include a generally block-shaped housing in which lasers, photodiodes and associated electronic circuitry are enclosed, and a connector that can be plugged into or otherwise mated with a connector mounted on the surface of the circuit board. An optical cable comprising one or more optical fibers may pass through the upper portion of the housing or be attached to a connector on the upper portion the housing and be optically coupled to the lasers and photodiodes. Some opto-electronic modules of this type include an array of multiple lasers and photodiodes. The connector on the bottom of such an opto-electronic module can include an array of electrical contacts. Grasping the housing, a person can press the module down onto a mating connector that is mounted on the surface of the circuit board until the connector on the bottom of the module is mated with the corresponding connector on the circuit board. When mated or connected in this manner, multiple electrical signals can be passed in parallel between the opto-electronic module and the circuit board.
One challenge in developing a mid-board opto-electronic module of the type described above has been retaining the module in the mated position. Some modules include holes through which mounting screws can be passed to screw the module down against the circuit board.
Another challenge in developing opto-electronic modules has been providing adequate shielding against electromagnetic interference (EMI). The signals that pass through the mated connectors between the module and the circuit board are susceptible to EMI. In an edge-mounted module arrangement, the front panel opening or receptacle in the system enclosure or rack into which the module is plugged can in some instances be shielded by, for example, providing EMI-shielding contact fingers around the periphery of the opening. However, providing adequate yet economical EMI shielding for a mid-board opto-electronic module can be more challenging.